A motor controller for an electric vehicle in the related art controls a motor current so that torque generated by a motor follows a torque command in response to an accelerator operation of a driver.
Furthermore, the motor controller for the electric vehicle suppresses vibrations which are generated by torque ripples generated in the motor during creep travelling of the vehicle being coincident with a resonance frequency of torsional vibrations of the vehicle, and vibrations generated by motor torque steeply rising during a sudden start of the vehicle. In this manner, it is required to provide a comfortable ride for the driver.
In the motor controller for the electric vehicle in the related art, various proposals have already been made in order to achieve the above-described object. For example, there is provided a method in which a first torque target value set based on various vehicle information items of a vehicle is input to a filter including characteristics corresponding to a model Gp(s) which inputs torque to the vehicle and has a transfer characteristic of a motor rotation speed so as to calculate a rotation speed estimation value of a motor. Then, a difference between the rotation speed estimation value of the motor and a rotation speed detection value detected by motor rotation speed detection means is calculated, and is input to a filter including a model H(s)/Gp(s) using a band-pass filter H(s) having the transfer characteristic in which a difference between a denominator order number and a numerator order number becomes equal to or greater than a difference between a denominator order number and a numerator order number in the above-described model Gp(s). In this manner, a second torque target value is calculated, and the second torque value is added to the first torque value so as to create a new motor torque command value (for example, refer to PTL 1).
In addition, there is an alternative method in which a speed variation of the motor is extracted by means of the fast Fourier transform so that a vibration frequency component selected based on the extraction result is fed back to a motor torque command, thereby suppressing tire shaft vibrations and motor shaft vibrations (for example, refer to PTL 2).
In addition, there is another method of reducing vibrations by suppressing torque ripples of the motor. In this method, a table relating to amplitude and a phase of the torque ripples corresponding to the torque generated by the motor is created, and a ripple compensation value corresponding to a torque command value is calculated so as to suppress the amplitude and the phase of the torque ripples with reference to the table. In this manner, the motor shaft vibrations generated by the torque ripples are suppressed (for example, refer to PTL 3 and PTL 4).
As still another method, when a rotary electric machine is used as a drive source of the vehicle, for example, in some cases, the torque ripples having different characteristics are generated due to variations in the characteristics of mount rubber of a support unit for supporting the rotary electric machine in a vehicle body, or a structure of a drive transmission system from the rotary electric machine to wheels. In this case, since the generated torque ripples are different between a forward movement and a rearward movement of the vehicle, there is provided a positive/negative determination unit which determines positive or negative output torque of the rotary electric machine. In this manner, the vibrations of the vehicle are suppressed by generating a ripple correction wave having different phases corresponding to the positive or negative output torque, and by performing proper ripple correction corresponding to the generated torque ripples (refer to PTL 5).
PTL 1: Japanese Patent No. 3508742
PTL 2: Japanese Patent No. 4787736
PTL 3: Japanese Patent No. 3242223
PTL 4: JP-A-2005-247574
PTL 5: Japanese Patent No. 4835959
NPL 1: Karikomi et al., Highly Responsive Acceleration Control for Newly Developed EV, Society of Automotive Engineers of Japan, Annual Conference Proceedings No. 55-11